1. Field of the Invention
This invention is concerned with the manufacture of light olefin hydrocarbons from lower alcohols and/or their ethers. It is particularly concerned with the catalytic conversion of such alcohols and ethers selectively to mixtures of olefins having up to five carbon atoms. In another aspect, this invention is concerned with a novel catalytic process especially effective for the substantially complete conversion of methanol and/or dimethyl ether to a hydrocarbon mixture characterized by a predominance of olefins.
2. Description of Prior Art
A remarkable growth in the production of synthetic fibers, plastics and rubber has taken place in recent decades. This growth, to a very large extent, has been supported and encouraged by an expanding supply of inexpensive petrochemical raw materials such as ethylene, propylene, and other four and five carbon olefins. Side by side with this remarkable development there has been an increasing demand for alkylate, made by reacting olefins with isobutane, for use as a high octane gasoline component. Environmental factors which limit the lead content of gasoline are likely to aggravate the need for alkylate and for other high-octane gasoline blending stocks.
Burgeoning demand for olefins, particularly ethylene, propylene and butenes, has of course led to periods of shortage, either due to short supply of suitable feedstocks, or to limited processing capacity. In any case, it would appear desirable to provide efficient means for converting raw materials other than petroleum to olefins and/or to high octane gasoline. The dehydration of alcohols, particularly ethanol to ethylene, by catalytic contact with the hydrogen exchanged form of mordenite is disclosed in U.S. Pat. No. 3,244,766, issued Apr. 5, 1966.
The production of olefins from methanol and dimethyl ether by limited conversion with HZSM-5 zeolite catalyst is described in U.S. patent application Ser. No. 537,043, filed Dec. 27, 1974 and now abandoned.
The use of a hydrocarbon diluent to dissipate exothermic heat in a two-stage conversion of methanol to gasoline is described in U. S. Pat. No. 3,931,349.
A two-stage conversion of methanol to olefins and to gasoline which employs a tubular reactor for the second stage is described in U.S. patent application Ser. No. 496,434, filed Aug. 9, 1974, and now abandoned.
U.S. Pat. No. 4,025,576 discloses a process for converting lower monohydric alcohols and their simple or mixed ethers to light olefins by contact with a zeolite catalyst.
U.S. Pat. No. 4,083,889 discloses the production of ethylene from methanol utilizing a zeolite catalyst.
U.S. Pat. No. 4,016,218 discloses the alkylation of aromatic hydrocarbons by contacting them with an olefin alkylating agent in the presence of a catalyst which can be a crystalline zeolite which has been modified by prior thermal treatment from an alpha in the range of 500 to 10,000 to an alpha of less than about 200 but greater than 10.
The processes directed to converting lower alcohols and ethers to olefins ordinarily utilize a fixed bed of catalyst. The feedstock containing methanol and dimethyl ether is introduced at one end of the zone and flowed through the zone whereas the conversion to light hydrocarbons is effected. An effluent stream containing the desired light olefins is removed from the bed.
We have now discovered that, in the catalytic conversion of alcohols to hydrocarbon compounds, particularly in the preparation of olefinic hydrocarbons, the activity of certain zeolite catalysts for olefin production can be desirably and dramatically increased by contacting the vaporized alcohol with certain zeolite catalysts which have been steamed from a higher alpha value to a lower alpha value and which has a crystal size less than one micron. The conversion of alcohols to olefins over the steam-treated small crystal zeolite when compared to conversion over an unsteamed zeolite is considerably enhanced even though the two zeolites compared have equivalent alpha values. For reasons that are not fully understood, it has been found that the crystal size of the zeolite is an important parameter which determines whether or not the activity of said zeolite for olefin production will be enhanced by steaming as will be demonstrated in the examples, zeolites, having a crystal size of one micron or greater do not show a "boost" or enhancement in activity for olefin production when steamed.